The Calcium Culprit: A Case of Denosumab-induced Hypocalcemia

Diagnosis and Management of Denosumab-Induced Hypocalcemia and Hypophosphatemia in the Setting of Metastatic Prostate Cancer

Denosumab, a receptor activator of nuclear factor kappa-Β ligand (RANK-L) monoclonal antibody used in osteoporosis and various malignancies, has been shown to cause hypocalcemia shortly after initiation of treatment. There have been few case reports of electrolyte abnormalities in patients managed with long-term treatment with this medication. This report presents the case of a 43-year-old male with metastatic prostate cancer who presented with severe hypophosphatemia and hypocalcemia, initially resistant to repletion. After more aggressive and persistent repletion with IV calcium, phosphorus, and vitamin D, as well as time for the denosumab to dissipate, the patient’s electrolytes stabilized and he was able to be discharged with oral replacement and close follow-up. Therefore, long-term monitoring of electrolytes for patients on denosumab should be carefully considered.

Denosumab-Induced Hypocalcemia after Billroth II Gastric Bypass Surgery

Hypocalcemia is a known risk following bariatric surgery and can contribute to the development of osteoporosis. Osteoporosis is commonly treated with denosumab, though denosumab can exacerbate underlying abnormalities in calcium homeostasis. We present the case of a 59-year-old female with severe hypocalcemia who had been treated with denosumab for osteoporosis three months before and had Billroth II gastric bypass surgery 15 years before, for bariatric purposes. Intravenous calcium supplementation was used to correct the initial electrolyte abnormality, and the patient was able to maintain appropriate calcium levels on high doses of oral calcium before discharge. Denosumab-induced hypocalcemia has been previously reported in patients with predisposing conditions including chronic kidney disease, primary sclerosing cholangitis, Crohn's disease, and a history of sleeve gastrectomy for marginal gastric ulcers. A few cases of hypocalcemia have been reported in patients with a history of bariatric surgery secondary to vitamin D deficiency, but this report is unique in demonstrating denosumab-induced hypocalcemia after bariatric surgery with normal vitamin D levels, suggesting a primary malabsorption of calcium. The risk of severe hypocalcemia should be considered before initiating denosumab to treat osteoporosis in patients with a history of bariatric surgery. If denosumab is initiated, serum calcium levels should be closely monitored, and patients should be educated about the importance of adherence to calcium supplementation.